The attachment of viruses to cell surface molecules is the initial step of virus replication and specific cellular virus receptors are, therefore, major determinants for virus tissue tropism. Decay-accelerating factor (DAF/CD55), a 70 kDa glycosyl phosphatidyl inositol (GPI) anchored complement regulatory protein consisting of four extracellular short consensus repeats (SCRs), serves as a membrane attachment protein for numerous human enteroviruses, including several echoviruses (EV), coxsackie B viruses (CVB) and Coxsackievirus A21 (CVA21). In general, viral binding to DAF alone is insufficient to permit enteroviral infections and interactions with DAF do not induce 135S altered (A) particles, which are considered to be a prerequisite for cell entry. The physiological role of DAF for enteroviral infections is postulated to be as a membrane sequestration receptor that binds and concentrates the infectious virus, resulting in increased opportunity for cell entry via interactions with a second functional cell entry receptor.
Like for many other picornaviral receptors (employed by polioviruses, the major receptor group rhinoviruses and coxsackie B viruses), the CVA21 cellular internalizing receptor, intercellular adhesion molecule-1 (ICAM-1/CD54), is a member of the immunoglobulin-superfamily and binds within the capsid canyon surrounding the fivefold axis. Interactions between the viral receptor at the base of the canyon destabilize the capsid and induce conformational changes, a prelude to viral uncoating.
The prototype strain of CVA21 (Kuykendall), a causal agent of respiratory infections, binds to both ICAM-1 and DAF. Binding of the prototype strain of CVA21 to surface expressed DAF is, however, not sufficient to initiate a productive infection or formation of A-particles, and interaction with ICAM-1 is required for cell entry. A more functional role for DAF during CVA21 infection is observed when surface DAF is cross-linked by a monoclonal antibody (mAb) directed against a non-viral binding domain of DAF, allowing infection in the absence of ICAM-1.
The present applicant previously developed new methods for treating malignancy using oncolytic viruses that recognise ICAM-1 (WO 01/37866). Excellent therapeutic results were obtained by using various Coxsackievirus A strains on a number of cancer cell types. In order to expand the possible cancer treatment and provide even more efficacious treatments, the present inventors have obtained new oncolytic viruses with improved oncolytic and killing properties by modification and bioselection.